A. Field of the Invention
This invention relates to the field of wheelchairs which have adjustability features to accommodate the physical size and comfort of the wheelchair user. More particularly, this invention relates to a wheelchair providing (1) wheelchair frame width adjustment, (2) wheelchair rear axle position adjustment, (3) wheelchair seat height and bucketing angle adjustment, (4) wheelchair seat base width and length adjustment, (5) wheelchair seat back angle-adjustment and (6) wheelchair seat fore and aft position adjustment. The invention also includes a truss structure wheelchair caster fork for attaching a caster wheel to a wheelchair.
B. The Background Art
In the prior art, caster wheels were used on wheelchairs, but they were typically heavy, unsightly and expensive. FIGS. 8-10 depict prior art wheelchair casters.
In prior wheelchair frames, the width or the distance between the wheelchair wheels was typically set during manufacture. Wheelchairs were made in different widths by lengthening or shortening the cross member tubes. A user of a prior wheelchair generally could not make any wheelchair frame width adjustment after purchase of the wheelchair.
A few prior wheelchairs have been capable of limited width adjustment by the use of replaceable cross members or length-adjustable cross members. This adjustment was only possible, however, on parallel-side frame wheelchairs with frames designed with such adjustment in mind (e.g., folding chairs), but not on rigid tubular wheelchair frames or on shell or parallel-plate truss structure wheelchair frames. The adjustment provided by prior wheelchairs was difficult for the user of a wheelchair to make without assistance and often difficult to set accurately. Further, structural strength of prior wheelchairs was adversely affected by such width adjustment mechanisms.
Some prior wheelchairs have adjustable rear wheel axle positioning. Axle adjustment in the prior is typically accomplished by (1) having multiple axle receiver holes for installation of the axle in various positions, (2) having a single axle receiver hole in a lug that can be moved to a number of different holes in the wheelchair frame or in an attachment to the wheelchair frame, or (3) having a lug attached to a horizontal slot in a plate, the plate being bolted to the tubes of the wheelchair frame. These prior axle positioning adjustment features may provide horizontal or vertical adjustment or both. These prior axle adjustment systems typically offered limited adjustment, were difficult to use and prone to inaccurate adjustment, and often lacked the strength and durability of non-adjustable axle assemblies.
Typical prior wheelchairs do not offer adjustment of the wheelchair seat relative to the wheelchair frame. U.S. Pat. No. 5,176,393 to Robertson et al. (which is hereby incorporated by reference in its entirety) provides height adjustment by using a seat mounted on telescoping tube assemblies. No other prior seat height adjustment or bucketing angle adjustment (if only the front or rear of the seat adjusts) features are known. Instead of providing seat height adjustment, many prior wheelchairs offered footrests with telescoping length adjustment. The one known prior height and bucketing angle adjustment mechanism was inadequate in the range and type of adjustment offered, and it tended to slip out of adjustment over time.
Seat base width and length in the prior was set at the time of wheelchair manufacture because all known prior wheelchairs used the wheelchair frame members as a base for the seat. Thus because the frame width and length could not be adjusted, the seat base width and length could not be adjusted. These adjustments are desirable because of the wide variations in dimensions of various people and the tendency of the dimensions of any particular person to change over time.
Some prior wheelchair manufacturers offered the wheelchair user the opportunity to specify a seat back angle which would be incorporated into the wheelchair at the time of manufacture. Thereafter, seat back angle was fixed and could not be adjusted. A few prior wheelchairs offered a reclinable seat back feature, but none offered fine, non-reclining seat back angle adjustment. Thus, effective non-reclining adjustment of seat back angle was absent from the prior wheelchairs.
The fore and aft position of a wheelchair seat relative to the wheelchair frame and associated change in the center of gravity of the wheelchair for user comfort and wheelchair stability was not known in the wheelchair art prior to the invention.
The lack of substantial adjustability of prior wheelchairs results in most wheelchair users suffering from poor wheelchair fit, increased difficulty achieving mobility, physical discomfort, and even some degradation of physical condition. A wheelchair readily adaptable to the ergonomic needs of wheelchair users was not available in the prior wheelchairs.